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Exploring Directional Differences In Resistivity Results In Karst
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 18th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Apr 2005, cp-183-00133
Abstract
We are involved in a multi-year study to evaluate electrical resistivity as a tool to characterize<br>shallow karst. As part of this study, we have conducted a 56-line multielectrode resistivity survey (28 x<br>28 grid of tests) and a 12-line azimuthal survey on a site with a known cave and other karst features.<br>(The cave is located at the approximate center of the grid and at the center of the azimuthal tests.) In the<br>inversion results for these lines, the air-filled cave appears to be a high resistivity feature when the tests<br>are run perpendicular to geologic strike and a low resistivity feature when the tests are conducted<br>parallel to strike. We have used data from borings taken at the site and an understanding of karst<br>geology to develop a subsurface model that results in similar anomalous results when used as data for a<br>resistivity forward modeling program. We conclude that the fracture patterns in the rock and water in<br>the vadose zone create the conditions causing the anomalous results observed and propose an<br>investigation approach that would help identify such conditions in the field.